Solid-state electroluminescent moving display device

ABSTRACT

A device for providing a moving display having an electroluminescent phosphor layer arranged to emit a band of light when alternating current voltages of different amplitudes are applied across the phosphor layer. A layer having a plurality of electrodes separated by transparent resistive material is positioned at one side of the phosphor layer and a common electrode layer is positioned at the opposite side of the phosphor layer. The voltages are applied to the electrodes and to the common electrode layer and the amplitudes of the voltages are changed sequentially to cause the band of light to move in a direction and at a speed in accordance with the sequence and rate of change in the amplitudes of the voltages.

waited States Patent Sylvander [151 3,641,533 [451 Feb. 8, 1972 [54]SOLID-STATE ELECTROLUMINESCENT MOVING DISPLAY DEVICE [72] Inventor:Frederick B. Sylvander, Rutherford, NJ.

[73] Assignee: The Bendix Corporation [22] Filed: June 26, 1969 [21]Appl. No.: 836,704

3,234,531 2/1966 Cleaver ..340/198 3,479,646 11/1969 Requa ..340/3243,525,091 8/1970 Lally ...340/324 3,379,927 4/1968 Yando ..3l5/55 [57]ABSTRACT A device for providing a moving display having anelectroluminescent phosphor layer arranged to emit a band of light whenalternating current voltages of different amplitudes are applied acrossthe phosphor layer. A layer having a plurality of electrodes separatedby transparent resistive material is positioned at one side of thephosphor layer and a common electrode layer is positioned at theopposite side of the phosphor layer. The voltages are applied to theelectrodes and to the common electrode layer and the amplitudes of thevoltages are changed sequentially to cause the band of light to. move ina direction and at a speed in accordance with the sequence and rate ofchange in the amplitudes of the voltages.

5 Claims, 22 Drawing Figures CO/VDUCT/l E MATER/AL SOLID-STATEELECTROLUMINESCENT MOVING DISPLAY DEVICE BACKGROUND OF THE INVENTIONField of the Invention CROSS-REFERENCE TO A RELATED U.S. PATENT Thepresent invention is directed. to improvements in solidstate devices ofa type providing illuminated moving displays such as that disclosed in aU.S. Pat. No. 3,543,083, granted Nov. 24, 1970 on a US. application Ser.No. 668,099 filed Sept. 15, 1967 by Frederick Blancke Sylvander,inventor of the present invention, and assigned to The BendixCorporation, assignee of the present invention. In the form of theinvention disclosed in the US. Pat. No. 3,543,083, there is provided apiezoelectric material in generating standing waves of vibrations toachieve the moving display. The piezoelectric material is difficult tomachine while the generation of the standing waves required anexcitation alternating current voltage having a frequency equal to theresonant frequency of the piezoelectric material. Temperature changeschanged the resonant frequency of the piezoelectric material to theextent that the excitation voltage was unable to cause the piezoelectricmaterial to generate the standing waves.

The present invention overcomes the disadvantages of difficultmanufacturing and temperature sensitivity by eliminating the need forstanding waves of vibration, and hence the piezoelectric material. Thepresent invention is directed to an improvement in the display device ofthe type including a layer of electroluminescent phosphor, together withmeans for applying across the phosphor layer alternating voltages havinga gradient along the phosphor layer to provide the symbol, as describedand claimed broadly in the US. Pat. No. 3,543,083. However instead of apiezoelectric material being provided in the means for applying thealternating voltages across the layer of electroluminescent phosphor, asin the specific form of the invention disclosed in the US. Pat. No.3,543,083, in the improvement of the present invention there areprovided in the means for applying the alternating voltages across thelayer of electroluminescent phosphor, a plurality of electrodesseparated by resistive material so that alternating current voltageshaving different sequential changing amplitudes, related to the lightemitting threshold level of electroluminescent phosphor, may besimultaneously applied across the electroluminescent phosphor to achievea display symbol that moves in a direction and at a rate in accordancewith the sequence and the rate of change of the amplitudes.

SUMMARY OF THE INVENTION A device for displaying a moving symbolcomprising an electroluminescent phosphor. A layer having a plurality ofelectrodes separated by resistive material is positioned at one side ofthe phosphor layer and a common electrode layer is positioned at theopposite side of the phosphor layer. Alternating current voltages areapplied to the electrodes and to the common electrode layer to providethe symbol. The amplitudes of the voltages are changed sequentiallycausing the symbol to move in a direction and at a speed in accordancewith the sequence and rate of change of the alternating currentvoltages.

Oneobject of the present invention is to provide a solidstateelectroluminescent moving display device operative over a widetemperature range.

Another object of the present invention is to provide a device that iseasy to manufacture.

Another object of the present invention is to provide a solidstatedevice displaying a linear moving symbol.

Another object of the present invention'is to provide a solidstatedevice displaying a two-dimensional moving symbol.

Another object of the present invention is to provide a solidstatedevice display a circular moving symbol.

The foregoing and other objects and advantages of the invention willappear more fully hereinafter from a consideration of the detaileddescription which follows, taken together with the accompanying drawingswherein three embodiments of the invention are illustrated by way ofexample. It is to be expressly understood, however, that the drawingsare for illustration purposes only and are not to be construed asdefining the limits of the invention.

DESCRIPTION OF THE DRAWINGS FIG. I shows a novel solid-stateelectroluminescent device constructed in accordance with theinventionfor displaying a one-dimensional moving symbol.

FIG. 2 shows a system using the display device shown in FIG. 1 forproviding a moving display corresponding to the relative angularvelocities of two devices, such as on an aircraft.

FIG. 3 shows three voltage outputs from the synchro differentialtransmitter in the display system shown in FIG. 2.

FIGS. 4A, 4B and 4C show a moving symbol in the fonn of a band of lightin response to applied changing voltages in the display system shown inFIG. 2.

FIG. 5 shows another embodiment of the invention for providing acircular moving display.

FIG. 6 is a sectional view of the device shown in FIG. 5 along the line6-6 as viewed in the direction of the arrows.

FIG. 7 shows the electrode and resistive material layer of the deviceshown in FIG. 5.

FIG. 8 shows a solid-state electroluminescent device similar to thedevice shown in FIG. 1 for displaying a two-dimensional moving symbol.

FIG. 9 shows a system using the display device of FIG. 8 for displayinga two-dimensional moving symbol corresponding to conditions, such as thepitch and yaw of an aircraft.

FIGS. 10A and 108 show six voltage outputs from the synchros in thedisplay system shown in FIG. 9.

FIGS. llA through 111 show a moving two-dimensional symbol in accordancewith the applied alternating current voltages in the display system ofFIG. 9.

DESCRIPTION OF THE INVENTION Referring to FIG. 1, there is shown a novelsolid-state electroluminescent device 1 for displaying a moving symboland having a layer 3 of conductive material, such as aluminum, connectedto a terminal 4 connected to ground. The layer 3 may be transparentalthough this is not essential. A layer 8 of an electroluminescentphosphor is affixed to layer 3 of conductive material. Theelectroluminescent phosphor may be zinc sulfide or cadmium sulfideactivated by copper, gold or silver. The electroluminescent phosphoremits light when subjected to an alternating current voltage greaterthan the light emitting threshold level of the electroluminescentphosphor.

A layer I4 having electrodes 15, 15A and 15B separated by transparentresistive material 18, such as stannous chloride, nichrome or gold, isaffixed to layer 8 of electroluminescent phosphor for controlling theilluminating of the electroluminescent phosphor. The thickness of thetransparent resistive material 18 determines its resistivity andtransparency. Terminals 20, 20A and 20B receive alternating currentvoltages and are connected to electrodes 15, 15A and 15B, respectively.At least one of the alternating current voltage applied to terminals 20,20A and 2013, but not all of the applied alternating current voltages,should have an amplitude greater than the light-emitting threshold levelof the electroluminescent phosphor. It is preferred that the amplitudesof alternating current voltages applied to terminals 20, 20A and 208 berelated to each other so that a band of light, emitted by theelectroluminescent phosphor in response to the applied alternatingcurrent voltages, has a constant width. A layer 21 of transparentnonconductive material, such as glass, is affixed to electrode andresistive material layer 14 to protect layer 14 while permitting viewingof the electroluminescent phosphor and to support layers 3, 8 and 14.

Layer 21 of a transparent material may be affixed to conductive layer 3instead of to electrode and resistive material layer 14, as heretoforementioned. When display device 1 is so constructed, it is immaterialwhether the transparent material in layer 21 is conductive ornonconductive.

Voltage gradients exists between electrodes 15, 15A and 158 whenalternating current voltages, such as heretofore described, are appliedto terminals 20, 20A and 208 due to transparent resistive material 18.The portion of the electroluminescent phosphor of layer 8 subjected to agreater than threshold voltage has a larger area, due to a voltagegradient, than it would have if insulation separated electrodes 15, 15Aand 158. The increase in area of the electroluminescent phosphor oflayer 8 emitting light causes device 1 to display a band of light havinga larger width for ease of viewing.

Referring to FIG. 2, there is shown, for purpose of illustration, oneuse of display device 1 for providing a linear display corresponding tothe difference in speed of rotation between two propellers on anaircraft. A propeller 23 is connected to a rotor winding 25 of analternating current synchro transmitter 26 and drives rotor winding 25at a rotational speed w, corresponding to the rotational speed ofpropeller 23. Rotor winding 25 of synchro 26 is energized by analternating current voltage E,. Synchro 26 is a conventional typesynchro transmitter and has common connected stator windings 30, 31 and32 providing output signals corresponding to the rotation of rotorwinding 25.

Stator windings 30, 31 and 32 are connected to stator windings 35, 36and 37, respectively, of a conventional type differential synchrotransmitter 40 having rotor windings 43, 44 and 45 commonly connected toground. A second propeller 47 is connected to rotor windings 43, 44 and45 of synchro 40 and drives rotor windings 43, 44 and 45 at a rotationalspeed corresponding to the rotational speed of propeller 47. Rotorwindings 43, 44 and 45 of synchro 40 provide voltage E E and E as shownin FIG. 3, corresponding to the difference in speeds a), and m of rotorwindings 25 and 43, 44 and 45.

Rotor winding 43, 44 and 45 of differential synchro transmitter 40 areconnected to terminals 20, A and 20B, respectively, of display device 1having terminal 4 connected to ground and alternating current voltages EE and B are applied thereto. When the rotational speed of propellers 23and 47 are the same, device 1 displays a stationary band of light. Whenpropellers 23 and 47 rotate at different speeds, the band of light movesin a direction corresponding to the propeller which has the fastestrotational speed and the band of light moves at a speed corresponding tothe difference in the rotational speeds of the propellers 23 and 47, ashereinafter explained.

Referring to FIGS. 2, 3 and 4, for purposes of illustration, when thepropellers of the aircraft are rotating at the same speed, rotationalspeed m of rotor winding of synchro transmitter 26 is equal torotational speed (0 of rotor windings 43, 44 and 45 of differentialtransmitter 40 causing alternating current voltages E E and 13,, appliedto display device 1, to remain constant in amplitude as if received froma synchro whose rotor winding is stationary. This results in displaydevice 1 providing a centered band of light on the display as shown inFIG. 4A. The voltages E;,, E, and E have the following relationships:

E E, sin (m -m A difference in propeller speeds w, and m causes voltagesE E and E to appear as voltages from a synchro having a rotating rotorwinding. The changing amplitudes of voltages E E and E causes the bandof light to move in a direction, as shown by the arrows in FIGS. 48 or4C, determined by which propeller is rotating faster and at a rate inaccordance with the difference in propeller speeds as hereinafterdescribed. A small difference in propeller speeds results in the band oflight moving slowly, while a large difference causes the band of lightto move fast. With the relative motion of the propellers, the band oflight moves in one direction ofl the scale at either the upper or lowerend and returns at the lower or upper end, respectively, and provides acontinuously moving display.

If two of the three applied alternating current voltages have amplitudesgreater than the light emitting threshold of the electroluminescentphosphor, display device 1 will appear as an illuminated device with adark band that appears to move in a direction determined by whichpropeller is rotating faster and at a speed in accordance with thedifference in propeller speeds.

Referring to FIGS. 5, 6 and 7, there is shown a display device 50cylindrical in shape for displaying circular movement and having acircular layer 51 of conductive material connected to a terminal 54. Acircular layer 56 of electroluminescent phosphor, such as used indisplay device 1, is affixed to conductive material layer 51. A circularlayer 58 having electrodes 60, 60A and 60B, separated by transparentresistive material 61 as shown in FIG. 7, is affixed to theelectroluminescent phosphor layer 56. Electrodes 60, 60A and 60B areconnected to terminals 65, 65A and 658 which receive alternating currentvoltages E E and E but not all voltages, has an amplitude greater thanthe light emitting threshold level of the electroluminescent phosphor. Acircular layer 67 of transparent material, such as glass, is affixed tothe electrode and resistive material layer 58 to protect layer 58, whilepermitting viewing of the electroluminescent phosphor, and to supportlayers 51, 56 and 58.

Device 50 may be used in a system such as shown in FIG. 2 where voltagesE E and E from synchro 40 are applied to terminals 65, 65A and 653,respectively, of device 50. A band of light emitted byelectroluminescent phosphor in layer 56 of display device 50 moves in acircle in a direction determined by which propeller 23 or 47 is rotatingfaster and at a speed in accordance with the difference betweenpropeller speeds as heretofore explained for the operation of displaydevice 1.

Referring to FIG. 8, there is shown a display device 70 which is anotherembodiment of the invention. Display device 70 is similar to displaydevice 1 and has the same layers except that an electrode and resistivematerial layer 71, which is similar to electrode and resistance layer 14of display device 1, has additional electrodes 74, 74A and 74B,spacially related to electrodes 15, 15A and 15B. Terminals 75, 75A and75B are connected to electrodes 74, 74A and 743, respectively. Electrode74, 74A and 74B are shown in two parts which are electrically connectedtogether and insulated from electrodes 15, 15A and 158. The arrangementof electrodes 15, 15A, 15B, 74, 74A and 748 provides a two dimensionalsymbol on display device 70 in response to alternating current voltagesapplied to terminals 20, 20A, 20B, 75, 75A and 758 as hereinafterexplained. At least one alternating current voltage applied to terminals20, 20A and 20B and one alternating current voltage applied to terminals75, 75A and 758 must have an amplitude greater than the lightemittingthreshold of the electroluminescent phosphor of layer 8.

Referring to FIG. 9, 10A and 108, there is shown, for purposes ofillustration, one use of display device 70 shown in FIG. 2, in which asystem displays a symbol whose movement corresponds to the pitch and theyaw of an aircraft. A pitch sensor and a yaw sensor 82 provide signals Eand E respectively, corresponding to the pitch and yaw of the aircraft.

Signals E and E are applied to conventional type amplifiers 84 and 85,respectively, which provides signals E and E, signals to motors 88 and89, respectively. The rotational speeds of the shafts of the motors 88and 89 correspond to signals E and E Tachometers 90 and 91 aremechanically connected to the shafts of motors 88 and 89, respectively,and provide feedback signals to amplifiers 84 and 85 for maintaining therotational speed of motors 88 and 89 in accordance with signals E and EMotors 88 and 89 are used to rotate rotor windings 92 and 93 of synchros95 and 96, respectively, at speeds corresponding to pitch signal E andyaw signal E Rotor windings 92 and 93 of synchros 95 and 96,respectively, are energized by an alternating current voltage E Synchros95 and 96 have stator winding 102, 103 and 104 and 107, 108 and 109,respectively, commonly connected to ground. Stator windings 102, 103 and104 or synchro 95 provide voltages E E and E as shown in FIG. A, toterminals 20, A and 20B, respectively, of display device 70 inaccordance with the angular position of rotor winding 92. Statorwindings 107, 108 and 109 of synchro 96 provide voltages E E and E asshown in FIG. 103, to terminals 75, 75A and 75B of display device 70 inaccordance with the angular position of rotor winding 93.

Referring to FIGS. 9 and 11A through 11G, when the aircraft is notmoving about its pitch or yaw axis, display device 70 provides astationary light symbol such as shown in FIG. 1 1A. When the aircraftmoves about the pitch axis, the changing amplitudes of voltages E E andE causes the symbol to move in a direction, as shown by the arrows inFIGS. 118 or 11C, determined by the pitch direction and at a rate inaccordance with the pitch angle. When the aircraft moves about the yawaxis, the changing amplitudes of voltages E E and E causes the symboltomove in a direction, as shown by the arrows in FIGS. 11D or 1 1E,determined by the yaw direction and at a rate in accordance with the yawangle. When the aircraft moves about the pitch and yaw axes, thechanging amplitudes of voltages E E E E E and E causes the symbol tomove in a direction, as shown by the arrows in FIGS. 11F, 11G, 11H orIII, determined by the pitch and yaw directions and at a rate inaccordance with the pitch and-yaw angles. The shape of the symbol willchange as it moves, however the change is unimportant as device 70 willappear to display a moving symbol. With movement of the aircraft aboutthe pitch axis or the yaw axis, the symbol moves in one direction offthe scale at one end and returns at an opposite end and provides acontinuously moving symbol.

A solid state display device constructed according to the presentinvention is relatively easy to manufacture, is operative over a widetemperature range and provides a linear, a circular or a two-dimensionaldisplay.

While three embodiments of the invention have been illustrated anddescribed in detail, it is to be expressly understood that the inventionis not limited thereto. Various changes may also be made in the designand arrangement of the parts without departing from the spirit and scopeof the invention as the same will now be understood by those skilled inthe art.

What is claimed is:

1. In a device for displaying a moving symbol of a type including afirst layer of an electroluminescent phosphor having a light emittingthreshold voltage level, a second layer positioned at one side of thefirst phosphor layer, a third common electrode layer positioned at theopposite side of the first phosphor layer; wherein the improvementcomprises the second layer including a first set of a plurality ofelectrodes separated by transparent resistive material selected from agroup consisting of stannous chloride, nichrome and gold, means forapplying alternating current voltages of different amplitudes relatedone to the other simultaneously to the plurality of electrodes of thefirst set of electrodes and to the third common electrode layer, thealternating current voltage applied to one of said plurality ofelectrodes of the first set of electrodes having an amplitude greaterthan the light emitting threshold voltage level of theelectroluminescent phosphor of the first layer, and the alternatingcurrent voltage simultaneously applied to the other of said plurality ofelectrodes of the first set of electrodes being less than said thresholdvoltage level, the greater amplitude of the alternating current voltageapplied to said one electrode causing the first phosphor layer to emit aband of light to provide a symbol on the first layer ofelectroluminescent phosphor, and means for changing the amplitudes ofthe voltages simultaneously applied to said plurality of electrodes ofsaid first set so as to sequentially apply to each one of said pluralityof electrodes of said first set an alternating current voltage havingart amplitude greater than the light emitting threshold voltage level ofthe first phosphor layer to cause the emitted light band symbol to moveon the first layer of electroluminescent phosphor in a direction and ata speed in accordance with the sequence and rate of change of thealternating current voltages.

2. The improvement defined by claim 1 in which the means for changingthe amplitudes of the alternating current voltages across the firstlayer of electroluminescent phosphor includes a first signal devicehaving a rotor winding energized by an alternating current voltage, therotor of the first signal device being rotatable in accordance with afirst condition, the first signal device having stator windingsproviding output voltages in accordance with the rotation of the rotorwinding, another signal device having stator windings, the statorwindings of said other signal device being connected back to back to thestator windings of the first signal device and energized by the outputvoltages from the stator windings of the first signal device, and rotorwindings of the other signal device being commonly connected to thethird common electrode layer, the rotor windings of the other signaldevice being rotatable in accordance with a second condition to provideoutput voltages in accordance with a difference in the rotation of therotor winding of the first signal device and the rotation of the rotorwindings of the second signal device, and each rotor winding of thesecond signal device being connected to a corresponding electrode of theplurality of electrodes of the first set of the second layer to changethe voltages across the electroluminescent phosphor of the first layerin accordance with the output voltages from the rotor windings of thesecond signal device for causing the symbol to move on the first layerof electroluminescent phosphor in a direction and at arate in accordancewith the difference in said first and second conditions.

3. The improvement defined by claim 1 including each layer being acircular band, and the electrodes of the first set of the second layerbeing arranged in spaced relation with the selected transparentresistive material therebetween in the circular band of the second layerso that the symbol moves in a circle in the direction and at the speedin accordance with the sequence and rate of change of the alternatingcurrent voltage.

4. The improvement defined by claim 3 in which the second layer includesa second set of an additional plurality of electrodes and additionalselected transparent resistive material positioned between saidadditional electrodes, said second set of the additional electrodesbeing positioned in said second layer in a spaced axial relation to thefirst set of electrodes of said second layer, and in which thealternating current means applies alternating current voltages acrossthe second set of additional electrodes of said second layer, theelectroluminescent phosphor of the first layer and the third commonelectrode layer simultaneously with the application of alternatingcurrent voltages to the first set of electrodes of said second layer soas to effect a two dimensional display that moves in a direction and ata speed in accordance with the sequence and rate of change in theamplitudes of all the alternating current voltages.

5. The improvement defined by claim 4 in which the voltageamplitude-changing means includes two signal devices, each signal devicehaving a rotor winding energized by an alternating current voltage, eachrotor winding being rotatable in accordance with a different condition,and stator windings commonly connected at one end to the third commonelectrode layer and providing voltage outputs corresponding to therotathe first layer in accordance with the voltage outputs from thestator windings of the signal devices for causing the symbol on thefirst layer of electroluminescent phosphor to move in a direction and ata rate in accordance with a difference in said conditions.

1. In a device for displaying a moving symbol of a type including afirst layer of an electroluminescent phosphor having a light emittingthreshold voltage level, a second layer positioned at one side of thefirst phosphor layer, a third common electrode layer positioned at theopposite side of the first phosphor layer; wherein the improvementcomprises the second layer including a first set of a plurality ofelectrodes separated by transparent resistive material selected from agroup consisting of stannous chloride, nichrome and gold, means forapplying alternating current voltages of different amplitudes relatedone to the other simultaneously to the plurality of electrodes of thefirst set of electrodes and to the third common electrode layer, thealternating current voltage applied to one of said plurality ofelectrodes of the first set of electrodes having an amplitude greaterthan the light emitting threshold voltage level of theelectroluminescent phosphor of the first layer, and the alternatingcurrent voltage simultaneously applied to the other of said plurality ofelectrodes of the first set of electrodes being less than said thresholdvoltage level, the greater amplitude of the alternating current voltageapplied to said one electrode causing the first phosphor layer to emit aband of light to provide a symbol on the first layer ofelectroluminescent phosphor, and means for changing the amplitudes ofthe voltages simultaneously applied to said plurality of electrodes ofsaid first set so as to sequentially apply to each one of said pluralityof electrodes of said first set an alternating current voltage having anamplitude greater than the light emitting threshold voltage level of thefirst phosphor layer to cause the emitted light band symbol to move onthe first layer of electroluminescent phosphor in a direction and at aspeed in accordance with the sequence and rate of change of thealternating current voltages.
 2. The improvement defined by claim 1 inwhich the means for changing the amplitudes of the alternating currentvoltages across the first layer of electroluminescent phosphor includesa first signal device having a rotor winding energized by an alternatingcurrent voltage, the rotor of the first signal device being rotatable inaccordance with a first condition, the first signal Device having statorwindings providing output voltages in accordance with the rotation ofthe rotor winding, another signal device having stator windings, thestator windings of said other signal device being connected back to backto the stator windings of the first signal device and energized by theoutput voltages from the stator windings of the first signal device, androtor windings of the other signal device being commonly connected tothe third common electrode layer, the rotor windings of the other signaldevice being rotatable in accordance with a second condition to provideoutput voltages in accordance with a difference in the rotation of therotor winding of the first signal device and the rotation of the rotorwindings of the second signal device, and each rotor winding of thesecond signal device being connected to a corresponding electrode of theplurality of electrodes of the first set of the second layer to changethe voltages across the electroluminescent phosphor of the first layerin accordance with the output voltages from the rotor windings of thesecond signal device for causing the symbol to move on the first layerof electroluminescent phosphor in a direction and at a rate inaccordance with the difference in said first and second conditions. 3.The improvement defined by claim 1 including each layer being a circularband, and the electrodes of the first set of the second layer beingarranged in spaced relation with the selected transparent resistivematerial therebetween in the circular band of the second layer so thatthe symbol moves in a circle in the direction and at the speed inaccordance with the sequence and rate of change of the alternatingcurrent voltage.
 4. The improvement defined by claim 3 in which thesecond layer includes a second set of an additional plurality ofelectrodes and additional selected transparent resistive materialpositioned between said additional electrodes, said second set of theadditional electrodes being positioned in said second layer in a spacedaxial relation to the first set of electrodes of said second layer, andin which the alternating current means applies alternating currentvoltages across the second set of additional electrodes of said secondlayer, the electroluminescent phosphor of the first layer and the thirdcommon electrode layer simultaneously with the application ofalternating current voltages to the first set of electrodes of saidsecond layer so as to effect a two dimensional display that moves in adirection and at a speed in accordance with the sequence and rate ofchange in the amplitudes of all the alternating current voltages.
 5. Theimprovement defined by claim 4 in which the voltage amplitude-changingmeans includes two signal devices, each signal device having a rotorwinding energized by an alternating current voltage, each rotor windingbeing rotatable in accordance with a different condition, and statorwindings commonly connected at one end to the third common electrodelayer and providing voltage outputs corresponding to the rotation of therotor winding; each stator winding of one signal device being connectedat other ends to a corresponding electrode of the first set ofelectrodes of the second layer and each stator winding of the othersignal device being connected at other ends to a corresponding electrodeof the second set of electrodes of said second layer so as tosequentially change the applied voltages across the electroluminescentphosphor of the first layer in accordance with the voltage outputs fromthe stator windings of the signal devices for causing the symbol on thefirst layer of electroluminescent phosphor to move in a direction and ata rate in accordance with a difference in said conditions.